ON THE THEORY OF THE SPECTROPHONE

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Abstract
The spectrophone consists essentially of a constant gas volume that is exposed to intensity-modulated infrared radiation of a spectral range corresponding to one of the vibration–rotation bands of the gas.After a brief review of the history of the instrument a theoretical analysis of the processes in the spectrophone cell is presented on the basis of a two-state gas model. Expressions are derived for the time dependence of the upper-state population, of the gas pressure, and of the infrared absorption, emphasizing the effects due to a finite rate of exchange between vibrational and translational energy of the gas molecules. Numerical values are calculated for the 15-μ CO2 band and it is suggested that information on the mechanism of vibrational relaxation in polyatomic gases and gas mixtures can be obtained from experimental studies of the gas pressure in the spectrophone cell.

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